A protest against a third runway being built at Heathrow. The government has ruled out expansion at the airport. Photograph: Adrian Dennis/AFP/Getty Images

Aviation industry lobbyists have stepped up attempts to force the vexed question of a third runway at Heathrow back on to the agenda of an unwilling government, with unions and directors warning that inaction will cost thousands of jobs.

BAA-sponsored research by Oxford Economics claims Britain could lose out on more than 140,000 jobs if there is no clear support for a UK hub airport.

Len McCluskey, general secretary of the Unite union, said that decisive action was needed to maintain the airport's status. "Our economy desperately needs an airport infrastructure which is better than the patchwork provision we currently have around the capital," he said.

"Our politicians must think big and act in the national interest. We need an aviation strategy that acknowledges Heathrow as a hub, and we need it now."

The Institute of Directors also endorsed the research, which found that capacity constraints will cost the UK £4.5bn in GDP from foreign investment and £1.6bn in lost trade with emerging markets by 2021.

Mick Rix, of the GMB union, said it was "plain daft" to exclude the option of expanding Heathrow. "As this new research shows, there's an immediate need to safeguard the jobs and GDP that Heathrow provides."

The latest salvo in BAA's campaign for a third runway at Heathrow comes before this month's expected publication of the aviation white paper, which will discuss long-term strategy and options for airport capacity growth – possibly including a new hub in the Thames estuary.

More than 70 business leaders signed an open letter to chancellor George Osborne and transport secretary Justine Greening, published at the weekend in the Sunday Telegraph, demanding an aviation strategy for growth that "considers all options" – a thinly veiled demand to back Heathrow, for which a third runway was explicitly ruled out again in the autumn statement

BAA on Monday reiterated its threat to seek a judicial review if Heathrow is pre-emptively removed from consideration before any consultations on expanding airport capacity. It said: "None of the options for providing new hub capacity is easy, but all options should be on the table. It is important that major decisions by government follow due process and the option to seek a judicial review if they do not is always available. We expect the government to carefully consider the pros and cons of all options and consult properly before taking any policy decisions."

Environmentalists have been monitoring BAA's latest lobbying offensive, but the presence of Greening at the Department for Transport, who campaigned against a third runway, rules out imminent change for Heathrow. Moves toward expansion would make her position untenable.

At the official opening of London Southend airport on Monday, Greening insisted British airports were well placed to provide flights to the far east markets that BAA fears losing. "Any decision will need careful consideration," she said.

"If you were starting from scratch today, you would not put Heathrow where it is, and we need to look at how we can keep a competitive edge going forward."

John Stewart, chair of Hacan, which represents residents under the Heathrow flight path, said: "The argument has been settled. BAA will not accept that the current government rejected both the environmental and economic case for Heathrow expansion. It's a sign of its desperation that it has wheeled out Oxford Economics to do the report. These were the consultants who provided the economic basis for the now discredited 2003 air transport white paper."

Seema Malhotra, the recently elected MP for Feltham and Heston, a constituency under the Heathrow flight path, has tabled an amendment to the civil aviation bill to compensate residents for noise pollution.

• Justine Greening echoed the complaints of campaigners through the years that Heathrow was in the wrong place on Monday.

Asked to comment on the debate around the need for a new hub, including controversial plans for a new airport in the Thames Estuary, she insisted existing UK airports were well placed in providing flights to the far east.

But Greening added: "Any decision will need careful consideration. If you were starting from scratch today, you would not put Heathrow where it is, and we need to look at how we can keep a competitive edge going forward."

She was speaking at the opening of London Southend airport's new passenger terminal, where she stressed the importance of looking beyond the biggest airports serving London.

"The current debate on the future of aviation in our country as a whole has focused on hubs such as Heathrow and Gatwick.

"Our regional airports have an absolutely vital part to play in making sure the aviation sector remains competitive and continues to serve businesses and the community."